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COST Action FP1402
Basis of structural timber design - from research to standards
Short Term Scientific Mission Report
Measuring wind-induced vibration of tall timber buildings and towers
Applicant: Haoyu Huang
Department of Architecture and Civil Engineering, University of Bath, United Kingdom
Dates: 15th June 2015 – 1st July 2015 (15 days)
Host: Carsten Hein
Arup Berlin, Berlin, Germany
STSM reference number: COST-STSM-FP1402-28892
Contents
1. Purpose of the Short Term Scientific Mission (STSM) ........................................................................ 1
2. Description of the work carried out during the STSTM ...................................................................... 3
3. Description of the main results obtained ......................................................................................... 11
4. Conclusion ......................................................................................................................................... 14
5. Future collaboration with the host institution ................................................................................. 14
6. Foreseen publications ....................................................................................................................... 15
References ............................................................................................................................................ 15
COST Action FP1402: Basis of structural timber design - from research to standards
Title of STSM: Measuring wind-induced vibration of tall timber buildings and towers
STSM reference number: COST-STSM-FP1402-28892
STSM participant: Haoyu Huang
1
1. Purpose of the Short Term Scientific Mission (STSM)
As a widely used construction material, timber has been applied to building structures around the
world. With ongoing development and research in timber products and material science, today
timber has the potential to be widely used in tall structures. Tall timber buildings offer the benefits
of a sustainable, carbon storing material for the load-bearing as well as secondary structure, efficient
prefabrication and transport, a high quality interior climate and room atmosphere, and flexibility in
architectural design. The development of modern wood-based products like Glulam or CLT makes it
possible to improve material strength and create all types of construction elements like efficient
cross sections or timber-based slabs and plates. This opens up new possibilities for construction
types of timber buildings that have been applied in conventional high-rise buildings made of steel or
concrete using higher strength columns in frame construction or planar elements in solid timber
construction (Kolb et al., 2008).
The strength-weight ratio of timber is quite favourable compared to steel and concrete, which
makes it possible to also aim for economical buildings constructed of timber. However, one of the
key issues when designing a tall timber building is its lateral stiffness and response to horizontal
loads. Since timber buildings have a lower stiffness and inertia than conventional high-rise
structures, they are more sensitive to lateral loads and horizontal vibrations. Concerning the wind-
induced lateral movement of tall timber structure during normal operation, the vibration can cause
discomfort to residents or building occupants. Furthermore, wind-induced vibration can also lead to
the damage of non-structural elements. For timber buildings, these serviceability design criteria
might become decisive for much lower heights than for conventional tall buildings. Especially with
plans to increase the height of timber buildings even more, it is significant to study their dynamic
behaviour under wind load in design stage like it is done for conventional high-rise buildings. The
designer can access reference values given in design codes for e.g. the damping factor of steel and
concrete buildings depending on construction type. However, there is only little knowledge about
the dynamic properties of tall timber structures under wind load (Smith and Frangi, 2008, Reynolds
et al., 2015, BSI, 2005).
The key dynamic properties of a structure are natural frequency, lateral stiffness and damping
capacity. The natural frequency depends on the lateral stiffness and the mass of structure, e.g. Xue
et al. (2009) tested a 3-storey timber structure and found the natural frequency could be changed by
COST Action FP1402: Basis of structural timber design - from research to standards
Title of STSM: Measuring wind-induced vibration of tall timber buildings and towers
STSM reference number: COST-STSM-FP1402-28892
STSM participant: Haoyu Huang
2
adding bracings and causing damage to the structure. Brincker et al. (2004) demonstrated that the
natural frequency decreased with the increasing of mass. Damping ratio can present the ability in
energy dissipation. According to Reynolds et al. (2015), damping measurements are in dependence
of amplitude of excitation. It is important to get a deep understanding of the influence of structural
types, connection types, non-structural elements, excitation amplitude etc. on natural frequency,
lateral stiffness and damping capacity. Therefore, it is vital to study the performances of existing tall
timber buildings and towers exposed to wind-induced vibration so as to relate these to design stage.
Vibration testing of existing structures offers a great potential in gaining knowledge about dynamic
properties. There is a wide variety of methods to conduct the tests and to analyse data after
measurement. Experience has shown that ambient vibration testing is applicable to derive dynamic
properties of especially large, flexible structures with low natural frequencies and therefore suitable
for testing timber buildings. In contrast to forced vibration testing, ambient vibration testing makes
use of the natural vibrations of a structure. Therefore the structure does not have to be excited
artificially, which offers the advantages of higher efficiency, less disruption of the normal building
operation, no damage to the structural members and the possibility of a dynamic analysis under
normal conditions without influence of forced excitation (Geier, 2004, Reynolds et al., 2015).
The research group, which applicant belongs to, has already measured 5 multi-storey timber
structures in Italy, the UK and Sweden. A database has been built so as to inform engineers about
these important information. The data measured from the structures financed by this STSM can
greatly contribute to this database, because there are different types of timber buildings and towers
in Germany which can be thoroughly studied and compared. The host institute, ARUP Berlin, is a
leading institute for structural design, and has a professional group developing timber structures.
Through the collaboration with ARUP Berlin, they can provide the permission to LCT ONE building for
measurement and also the information from engineering aspects. Constructive suggestions from
ARUP Berlin concerning the measurements can help to close the gap between design practice and
academic research. The results from this STSM will inform the host institute the performances of
existing timber structures as well as their modal properties after analysis. Engineers can relate these
useful information to design criterion. From the view of research, the understanding of real
performances of timber structures helps the verification for structural modelling and explores the
potential for developing new structural forms and elements.
COST Action FP1402: Basis of structural timber design - from research to standards
Title of STSM: Measuring wind-induced vibration of tall timber buildings and towers
STSM reference number: COST-STSM-FP1402-28892
STSM participant: Haoyu Huang
3
2. Description of the work carried out during the STSTM
In this STSM, a total of 12 tall timber structures including timber towers and tall timber buildings in
Germany and Austria were measured in order to study the dynamic response. ARUP Berlin offered
the permission and information of LCT ONE, and advised during the selection of tall buildings and
towers in Germany.
2.1 Timber structures measured in this STSM
11 timber structures with different types in Germany and one in Austria were measured, and the
information are tabulated in Table 1. The locations of these timber structures are marked on a map
in Figure 1.
Figure 1 Locations of measured timber buildings and towers
COST Action FP1402: Basis of structural timber design - from research to standards
Title of STSM: Measuring wind-induced vibration of tall timber buildings and towers
STSM reference number: COST-STSM-FP1402-28892
STSM participant: Haoyu Huang
4
Table 1 Information of the timber structures measured in this STSM
Name of building/tower
Location Pictures Height [m]
Width [m]
Length [m]
Building LCT ONE Dornbirn, Austria
(Müller et al.)
26.8 12.2 23
KAMPA Aalen, Germany
(GmbH, 2015)
26.4 11.8 38
H8 Bad Aibling, Germany
24.4 12.1 21
Tower Altenbergturm Sulzbach-Laufen,
Germany
38.3 8.6 8.6
Himmelsstürmer Schwäbisch-Gmünd,
Germany
38.3 5.4 5.4
COST Action FP1402: Basis of structural timber design - from research to standards
Title of STSM: Measuring wind-induced vibration of tall timber buildings and towers
STSM reference number: COST-STSM-FP1402-28892
STSM participant: Haoyu Huang
5
Augstbergturm Trochtelfingen-Steinhilben,
Germany
20 4.4 4.4
Blumenthaler Aussichtsturm
Heiligengrabe, Germany
45 5 5
Timber Tower Hannover, Germany
100 7 7
Ochsenstiegl Thurmansbang, Germany
25 5.5 5.5
Aussichtsturm am Kadernberg
Schönberg, Germany
30 5.5 5.5
COST Action FP1402: Basis of structural timber design - from research to standards
Title of STSM: Measuring wind-induced vibration of tall timber buildings and towers
STSM reference number: COST-STSM-FP1402-28892
STSM participant: Haoyu Huang
6
Haidelturm Grainet, Germany
30 5.75 5.75
Baumturm Neuschönau, Germany
44 35.5 35.5
2.2 Measurement set-up
The equipment used in these vibration measurements can be divided into three parts, which
function in data input, data logging and data output, respectively. Data input part consists of three
piezoelectric accelerometers as shown in Figure 2 (a). They have a nominal sensitivity of 10V/g and a
lower frequency limit of 0.1Hz. The supports for the accelerometers are made of aluminium and are
heavy enough to prevent relative motion to the surface. The vibration acceleration can be recorded
in three dimensions in one point, or in one direction in three points. The data collected by the
accelerometers are saved in the data logger powered by a battery as presented in Figure 2 (b). A
software LABVIEW operated on the laptop in Figure 2 (c) can show the real-time vibration
acceleration, and is used for setting measurement duration and sampling rate. For each
measurement, the duration is 40 minutes. The final data exported from the laptop are acceleration
over time in the unit of 𝑚/𝑠2.
2.3 Measurement procedure
2.3.1 Timber buildings
For timber buildings measurement, the sensors are expected to be placed on the highest position of
the structure such as roof, as it helps to assess the highest vibration amplitude of the whole
structure especially in first mode shape. For some timber buildings like KAMPA building and H8
COST Action FP1402: Basis of structural timber design - from research to standards
Title of STSM: Measuring wind-induced vibration of tall timber buildings and towers
STSM reference number: COST-STSM-FP1402-28892
STSM participant: Haoyu Huang
7
building, the roof was hard to access because of the occupation of the solar power equipment, the
accelerometers therefore were placed on the top floor.
A reference measurement point was set in timber buildings measurement. As shown in Figure 3, the
measurement reference point is marked as B on the roof plan and top floor plan of LCT ONE building
and H8 building. For each point measurement, the reference point was measured in two horizontal
directions and measurement is able to be transformed into a common scale. In terms of the
concrete core or timber core in the timber structure, they play an important role in the lateral
vibration as they have higher stiffness than timber part; measurements in point A and point B
therefore can be compared (Figure 3). All measurement tests for timber buildings are tabulated in
Table 2.
Figure 2 Vibration measurement equipment (a) Accelerometers; (b) Data logger and battery; (c) Laptop
(a) (b)
(c)
COST Action FP1402: Basis of structural timber design - from research to standards
Title of STSM: Measuring wind-induced vibration of tall timber buildings and towers
STSM reference number: COST-STSM-FP1402-28892
STSM participant: Haoyu Huang
8
Concerning the long length in longitudinal direction of KAMPA building which is 38 meters, it is
important to measure, if asymmetrical movement occurs in short direction. Therefore,
measurement points were distributed along longitudinal length as seen in Figure 4 marked as C, D
and E, and the ambient vibration in short direction were measured. The same measurement was
done in H8 building as well. Points F, J and K allocated on 6th, 5th and 4th floor respectively were
measured in two horizontal directions in KAMPA building shown in Figure 4. Measurements in
different height can contribute to study the mode shape.
For each building, the timber floor vibration was also measured in order to examine the damping
capacity. The measurement duration was one minute, and the direction of accelerometer was
vertical. In the first half minute, the floor vibration was triggered by jumping for three times, and the
person walked around in last half minute.
Figure 3 (a) Roof plan of LCT ONE building; (b) Top floor plan of H8 building
(a) (b)
Y
X
Y
X
COST Action FP1402: Basis of structural timber design - from research to standards
Title of STSM: Measuring wind-induced vibration of tall timber buildings and towers
STSM reference number: COST-STSM-FP1402-28892
STSM participant: Haoyu Huang
9
Figure 4 Top floor plan of KAMPA building
Table 2 Summary of the measurements of timber buildings
Building Test Point Directions
LCT ONE building
1 A Y B (Reference point) X,Y
2 A X B (Reference point) X,Y
3 Top floor Vertical
H8 building
1 A X B (Reference point) X,Y
2 A Y B (Reference point) X,Y
3 C X D X E X
4 F Vertical
KAMPA building
1 A (Reference point) X, Y B Y
2 A (Reference point) X, Y
B X 3 C Y D Y E Y
4 C X D X E X
5 F Y G Y
Y
X
COST Action FP1402: Basis of structural timber design - from research to standards
Title of STSM: Measuring wind-induced vibration of tall timber buildings and towers
STSM reference number: COST-STSM-FP1402-28892
STSM participant: Haoyu Huang
10
H Y 6 F X G X H X
7 I Vertical
2.3.2 Timber Towers
There are 9 timber towers in Germany which were measured in this STSM. For timber towers, the
measurement is simpler, and the main measurement was only carried out in one point for three
directions. The time duration for each measurement was 40 minutes.
Figure 5 Timber Tower in Hanover (a) Outside view; (b) Inside view
It is worth mentioned that a timber wind turbine called Timber Tower was measured in Hanover as
seen in Figure 5. The influence of the blade rotation on vibration was studied in two tests; in the
first, the blade was moving and in the second its movement was restricted by shifting the blade.
For each tower, after 40-minute measurement, an additional test was carried out. An actively
induced vibration excited by shaking the tower at top floor for 20 seconds at its natural frequency as
well as the free vibration afterwards were measured. The natural frequency can be assessed
(a) (b)
COST Action FP1402: Basis of structural timber design - from research to standards
Title of STSM: Measuring wind-induced vibration of tall timber buildings and towers
STSM reference number: COST-STSM-FP1402-28892
STSM participant: Haoyu Huang
11
approximately through a fast Fourier transform (FFT) computation on site. The same active-induced
tests were done twice at two frequencies other than the natural frequency.
3. Description of the main results obtained
After measurements on these timber structures, acceleration over time in each channel has been
exported at a sampling rate of 200 Hz. A variety of analytical methods can be applied to obtain
structural dynamic properties from raw data, thus it is significant that these data from this STSM can
contribute to the database and engineers are able to download and analyse for their own purposes.
The key properties this report concerns are natural frequency and damping ratio which are closely
related to structural design and engineers are capable to compare these values with the predicted
from design criterion.
In this report, a better filter, the random decrement method and the flowing matrix pencil method
are employed for modal properties analysis. The function of a better filter is to reduce the noise at
high frequency and random decrement method extracts free vibration from ambient vibration (He
and Fu, 2001). Matrix pencil method is a frequency-domain analytical method using curve fitting for
free decaying wave, and natural frequency and damping ratio can be calculated (Zielinski and Duda,
2011). Results in flowing sections are computed using these methods operating in MATLAB.
3.1 Timber buildings
Analytical results of CLT ONE building designed by ARUP are shown here as an example. By analysing
the measurement data from point A in Figure 3 (a), structural response in frequency domain of X and
Y directions are plotted in Figure 6. Matrix pencil method is able to extract natural frequency and
damping ratio from modal curve fitting as shown in Figure 6 and these values are tabulated in Table
3. It can be seen that in longitudinal direction the structure has higher stiffness and damping
capacity as well as smaller vibration amplitude. The lateral stiffness therefore can be worked out by
estimating the mass of the structure based on the equation:
𝑓 =1
2𝜋√
𝑘
𝑚
COST Action FP1402: Basis of structural timber design - from research to standards
Title of STSM: Measuring wind-induced vibration of tall timber buildings and towers
STSM reference number: COST-STSM-FP1402-28892
STSM participant: Haoyu Huang
12
where 𝑘 and 𝑚 present the lateral stiffness and mass, and 𝑓 means the natural frequency in the unit
of Hz. Comparing the predicted natural frequency in design processes with the values of existing tall
timber structures, the over or less-estimation might be examined. It is vital that studies from
existing structures can give more understanding to analyse more accurate natural frequency and
damping capacity in design stage. For example, in the design of tuned mass damper (TMD), the
natural frequency of TMD should accurately depend on the natural frequency of the main structure
otherwise the efficiency would be reduced greatly.
Figure 6 Fitted spectrum in frequency domain of point A in (a) X direction; (b) Y direction
(a)
(b)
COST Action FP1402: Basis of structural timber design - from research to standards
Title of STSM: Measuring wind-induced vibration of tall timber buildings and towers
STSM reference number: COST-STSM-FP1402-28892
STSM participant: Haoyu Huang
13
Table 3 Analytical results of LCT ONE building
Directions Natural frequency (Hz) Damping ratio (%) Free decay spectrum amplitude (𝑚/𝑠2)
X 1.84 2.17 0.1244
Y 2.73 7.72 0.0463
The data can also be used in the research studying the effect of concrete core, timber core and shear
walls on structural performances. The torsion performances of the long timber structure like KAMPA
building can be studied using three distributed measurement points in one direction.
3.2 Timber towers
Same analytical methods are carried out on timber towers, and the frequency domain response of
Augstberg tower is shown in Figure 7 as an example. Because the structural shape of timber towers
is symmetrical, the results only show the measurement in one horizontal direction in this report. All
analytical results are presented in Table 4.
Figure 7 Fitted spectrum in frequency domain of Augstberg tower
Table 4 Natural frequency and damping ratio of all timber towers
Tower Natural frequency [Hz] Damping ratio [%]
Altenbergturm 1.88 2.24
Himmelsstürmer 1.65 1.07
Augstbergturm 2.74 2.10
COST Action FP1402: Basis of structural timber design - from research to standards
Title of STSM: Measuring wind-induced vibration of tall timber buildings and towers
STSM reference number: COST-STSM-FP1402-28892
STSM participant: Haoyu Huang
14
Blumenthaler Aussichtsturm 1.91 0.70
Timber Tower 0.33 0.78
Ochsenstiegl 1.99 2.08
Aussichtsturm am Kadernberg 2.15 1.39
Haidelturm 1.62 1.40
Baumturm 1.27 2.90
4. Conclusion
In this STSM, the wind-induced vibration measurements on 12 tall timber buildings and towers were
carried out in Germany and Austria. Through the collaboration with ARUP Berlin, different types of
tall timber structures were selected and studied. For buildings, ambient vibration in two horizontal
directions with reference point, ambient vibration along the structural length and height and excited
floor vibration were measured for duration of maximum 40 minutes at sampling rate of 200 Hz. In
terms of towers, three-dimensional measurements were carried out at the top. The data from this
STSM can contribute to the database which has been built by the institute the applicant belongs to.
Engineers can analyse these data using a variety of methods for their own purposes. The applicant
and the team belongs to focus on the structural dynamic properties such as natural frequency,
lateral stiffness and damping ration, and developed analytical methods in MATLAB for computation.
These values from existing tall timber structures can give engineers and researchers an
understanding how tall timber structure behaves in ambient vibration as there are short knowledge
currently. Further studies will be carried out and be related to the results of engineering design
practice.
5. Future collaboration with the host institution
In the meeting with Mr Carsten Hein and the timber group in Berlin, we discussed our further
collaboration and we are interested in the measurement of a timber building TCC designed by ARUP
in Münster. Based on the good collaboration between home institute and host institute, we agreed
to continue cooperation and more timber structures could be measured in the future.
COST Action FP1402: Basis of structural timber design - from research to standards
Title of STSM: Measuring wind-induced vibration of tall timber buildings and towers
STSM reference number: COST-STSM-FP1402-28892
STSM participant: Haoyu Huang
15
6. Foreseen publications
Based on the data from this STSM, further analytical methods aiming for noise reduction and
dynamic properties determination in frequency and time domain will be applied for different
purposes. Furthermore, studies for the influence of vibration amplitudes and types of construction
will be carried out in the future. It is hoped a journal paper will be published.
References
BRINCKER, R., RODRIGUES, J. & ANDERSEN, P. 2004. Scaling the mode shapes of a building model by
mass changes. IMAC-22: A Conference on Structural Dynamics. Hyatt Regency Dearborn, Dearborn,
Michigan, USA: Society for Experimental Mechanics.
BSI 2005. BS EN 1991-1-4:2005: Eurocode 1 – Actions on structures. Part 1–4: General actions –
Wind actions. London, UK: BSI.
GEIER, R. 2004. Brückendynamik: Schwingungsuntersuchungen von Schrägseilen, Books on Demand.
GMBH, B.-R. V.-M. 2015. KAMPA K8: Bis zur Hochhausgrenze aus Holz [Online].
http://www.regional-bauen.de/index.php?option=com_content&task=view&id=931.
HE, J. & FU, Z.-F. 2001. 9 - Modal analysis methods — time domain. In: HE, J. & FU, Z.-F. (eds.) Modal
Analysis. Oxford: Butterworth-Heinemann.
KOLB, J., LIGNUM & HOLZFORSCHUNG, D. G. F. 2008. Systems in Timber Engineering: Loadbearing
Structures and Component Layers, Birkhäuser.
MÜLLER, N., KAUFMANN, B., KAUFMANN, H. & STEINER, M. P. LifeCycle Tower - LCT ONE [Online].
http://www.hermann-kaufmann.at/pdfs/10_21.pdf.
REYNOLDS, T., HARRIS, R., CHANG, W.-S., BREGULLA, J. & BAWCOMBE, J. 2015. Ambient vibration
tests of a cross-laminated timber building. Proceedings of the ICE - Construction Materials [Online],
168. Available: http://www.icevirtuallibrary.com/content/article/10.1680/coma.14.00047.
COST Action FP1402: Basis of structural timber design - from research to standards
Title of STSM: Measuring wind-induced vibration of tall timber buildings and towers
STSM reference number: COST-STSM-FP1402-28892
STSM participant: Haoyu Huang
16
SMITH, I. & FRANGI, A. 2008. Overview of Design Issues for Tall Timber Buildings. Structural
Engineering International, 18, 141-147.
XUE, S., TANG, H., OKADA, J., HAYASHI, T., ZONG, G. & ARIKAWA, S. 2009. Natural frequency changes
for damaged and reinforced real structure in comparison with shake table and simulation. Materials
forum, 33, 344-350.
ZIELINSKI, T. P. & DUDA, K. 2011. Frequency and Damping Estimation Methods - an Overview.
Metrology and Measurement Systems, 18, 505-528.